In the Advanced Photo System (APS), transparent film base is coated on one surface with photographic emulsions and on the opposite surface with a virtually transparent layer of magnetic recording material that allows magnetic recording and reading of photographic data to and from the film strip utilizing a magnetic read/write head in the camera or photofinishing equipment or film scanner. As is well known in the magnetic recording art, debris consisting of dust and magnetic recording material builds up on the magnetic head and degrades the signal transfer performance of the read/write operation. The problem is more critical in a photographic system than in video or audio tape recording because the virtually transparent magnetic layer on film results in a lower strength magnetic signal on the film strip than can be achieved with thicker, more dense magnetic layers on video and audio tape. As a consequence, signal detection on film magnetic layers can be seriously degraded by microscopic buildup of debris on the magnetic head that might not produce noticeable effects in a video or audio tape recording system.
A known technique relied on for a degree of magnetic head cleaning in an APS camera is to rely on edges of film metering perforations formed in the film which are in line with thc film's magnetic data tracks to dislodge the debris built up on the camera magnetic heads. However, APS film has perforations only along one edge of the film. Equipment, such as film scanners which read data recorded in tracks along both edges of the film do not benefit from any cleaning action obtained from these perforations.
U.S. Pat. No. 5,715,488 proposes the use of a special perforation in the trailer portion of the film strip coupled with apparatus that ensures that the film is advanced past the last image frame sufficiently to cause the edges of the specially added perforation to rub across the magnetic head on that side of the film. Even so, it has been found that reliance on perforation edges to perform head cleaning is not entirely satisfactory.
U.S. Pat. No. 4,661,874 proposes forming a cleaning surface on tape by impressing the tape with a heated, ridged die to form rows of raised surfaces on the side of the tape opposite the side impressed by the die. This appears to be a type of embossment that creates raised surfaces on the cleaning side of the tape. While such embossed raised surfaces are somewhat effective in dislodging loosely accumulated debris from the heads, they prove to be relatively ineffective in removing debris clogs that are fused or burnished onto the head surface. U.S. Pat. No. 5,488,529 proposes a head cleaning photographic film that employs a "step difference" on the cleaning side of the film. In one embodiment, the step difference comprises either an integrally formed or adhesively applied 100 .mu.m raised area on the film surface as shown in FIG. 3b, (Example 2) Alternatively, this patent proposes that the step difference be a recess in the film, either in the form of a "through hole" (which is the same as a perforation as shown in FIG. 3b) or merely a "bottomed" hole (which is not further explained but would appear to be a hole that stops short of going all the way through the film). The "through hole" embodiment of this disclosure suffers from the same performance deficiency as the perforation of the '488 patent while the embossment embodiment has the same performance deficiency as the embossments of the '874 patent. The integrally formed and/or adhesively added projection, have the advantage of providing a raised edge to engage the debris on the head but has the disadvantages of providing only a single edge line to perform the cleaning operation, reducing its efficiency, and also of being difficult and costly to produce on film material.